Sintered tungsten carbide alloy product



United States Patent 3,000,087 SINTERED TUNGSTEN CARBIDE ALLOY PRODUCT Charles H. Dyer, Grand Junction, 'Colo., assignor to Western Alloy Products Company, Denver, Colo., a

corporation of Colorado No Drawing. Filed May 1, 1959, Ser. No. 810,227

9Clairns. (Cl. 29-1818) This invention relates to a sintered tungsten carbide alloy product, such product being particularly useful as or an insert for earth drilling tools, such as drill bits, jack hammer bits, and similar tools wherein resistance to abrasion and wear and also resistance to shock and impact are of particular importance.

Among the objects of this invention are to provide a novel sintered tungsten carbide alloy product; to provide such a product which may be formed as an insert for use in earth drilling tools; to provide such a product which is highly resistant to abrasion and wear and also to impact and shock; and to provide such a product which may be formed as any desired portion of an earth drilling tool.

Additional objects and the novel features of this invention will become apparent from the description which follows.

The more usual tungsten carbide is an apparent chemical combination having the approximate formula WC, made by first heating tungsten metal powder in a controlled atmosphere, such as of hydrogen to reduce the particle size, such as to about 4 microns. These particles are then carburized with a suitable form of carbon, such as lamp black, at an elevated temperature. These WC tungsten carbide particles are mixed with a binder, such as cobalt powder, in an amount, for instance, from 6% to 20% of the tungsten carbide, pressed and then sintered at a conventional elevated temperature to form a block of a desired shape in which the tungsten carbide particles are held together by a matrix of the binding agent. This sintered product may be used in the form of inserts or blocks, which are attached, as by silver solder, to the cutting face of an earth drilling tool, which may be used to drill or cut earth formations, such as in the case of earth drilling bits, jack hammer bits and the like. However, since the actual resistance to wear and abrasion depends upon the hardness of the insert itself, the hardness of the WC particles cannot be fully used. Thus, the resistance to impact and shock increases as the amount of the binding agent is increased, but any increase in the amount of binding agent decreases the hardness .and therefore the cutting qualities. As a result, a substantially maximum hardness of a tool or insert formed of sintered WC particles and a binding agentcannot be provided, since to do so would mean that the amount of binding agent, such as cobalt, must be reduced until the insert becomes so brittle that its resistance to shock and impact is lowered to such an extentthat the useful life of the tool is unduly reduced. For instance, an insert formed of WC powder and with 13% cobalt was found to have a hardness of 86 Rockwell A. Such an insert was resistant to shock and impact, but its hardness was less than the hardness of an insert formed of WC powder sintered with 6% cobalt and found to have a hardness of 91 Rockwell A. However, the latter insert was too brittle and therefore had insufllcient resistance to shock and impact.

The present invention is based upon the unexpected discovery that the useful life and the cutting qualities of a tool may be extended to a high degree by using particles of a tungsten alloy of W C and cobalt, having from 3.0% to 4% carbon, from 1% to 3% cobalt and the remainder tungsten, except for impurities up to a maximum of 3% and may include molybdenum, iron, etc. Thus, the tool or cutting portion thereof is formed as a sintered product formed from the above tungsten carbide cobalt alloy with a suitable binder, such as cobalt, iron, or nickel. All the particles maybe the tungsten alloy or a portion of the alloy with the remainder WC. Thus, the particles may be from 30% to 100% of the alloy and from-0% to of WC. Preferably, the proportions are from 40% to 60% of the alloy particles and the remainder WC particles. In one series of field tests, for instance, it was found that drilling bits, provided with inserts formed by pressing and sintering W C cobalt alloy particles with 13% cobalt binder, had a useful life of about four times that of otherwise identical tools, used for drilling the same earth formations, provided with inserts formed from pressing and sintering WC particles with 13% cobalt.

The alloy particles may be formed from the fused or cast tungsten alloy known as hard grade Haystellite, which is made from a tungsten having impurities up to 3%, including molybdenum which would ordinarily prevent satisfactory results for the present invention, and also does not have as high a degree of purity as the tungsten used in making WC particles. It will .be noted that a W C cobalt alloy having 9% cobalt has not been found suitable, and that the molybdenum cannotbe removed economically. However, the alloy for use in this invention may be made by placing such coarse tungsten particles, together with 1% to'3% cobalt particles, in an electric furnace and heating to a suflicient temperature to melt the tungsten powder by the heat of the arc of the carbon electrodes, which carbon from the electrodes and perhaps from lamp black, if added, apparently combines with the tungsten and the cobalt alloys therewith, in thefused product. This fused or cast product is then crushed and ground, as in a ball mill, to a suitable particle size. Thus, in the case of one type of W C cobalt alloy having 2% cobalt, in particles suitable for use in the present invention, about 10% of the particles were less than 4 microns in size, 20% of the particles were from 4 to 30 microns in size and the remainder, or 70%, was between 30 and 40 microns in size. Since tungsten powder has apparently not been successfully carbonized in sizes greater than 8 to 10 microns and usually in sizes of 4 microns and less, such as down to /2 micron, it will be evident that there will normally be a difference in the size of the particles of the W C cobalt alloy and WC. Thus, the WC particles are generally about 4 microns in size, while the W C cobalt alloy particles are generally larger in size. It will be understood, of course, that the .W C cobalt 'alloy particles may be greater than 40 microns or less than 10 microns in size. For example, when making a product of this invention used where erosion is a problem, as in hydraulic jet nozzles, it has been found desirable to mix WC particles with W C cobalt alloy particles, then place the mixture in a ball mill, for instance, and grind until the particle size may include a range of from 2 to 4 microns. However, for general use in earth drilling tools, it is normally unnecessary to grind to such fine sizes, ale

though the presence of such fine particles appears to be unobjectionable.

The W C cobalt alloy particles, or a mixture of W C cobalt alloy particles and WC particles, may be pressed with an appropriate amount of a binder, preferably cobalt, although iron, nickel, or alloys of cobalt, nickel, or iron may be used, or other suitable metallic binding agent having a melting point lower than that of WC and the W C cobalt alloy, then sintered at a suitable temperature to produce a suitable shaped insert or block or tool. For example, an insert for percussion bits formed of 60% W C cobalt alloy particles and 40% WC particles, with about 15% cobalt, based on the total weight of the W C cobalt alloy and WC particles, has been sintered at a temperature of 1450 C. For other proportions of W C cobalt alloy particles and WC particles, or of the binding agent, the sintering temperature may difier. The inserts may be rectangular or have any other desired shape, such as rectangular with a generally triangular apex which engagm the earth being drilled, and may be mounted on earth drilling tools in a suitable manner, as by the use of silver solder. Also, all or any desired portion of various types of earth drilling tools may be formed from. the sintered tungsten carbide product of the invention. Thus, the method of this invention for the production of a sintered tungsten carbide product is similar to the method previously used in the production of sintered WC products, but provides a new use of W C cobalt alloy particles.

A further unexpected result of this invention is that the inserts for rock bits, for instance, have been found to be self-sharpening. Thus, numerous inserts formed from a base of 60% W C cobalt alloy particles and 40% WC particles, with cobalt as a binder in an amount of 15% of the base, were found to have a Rockwell A hardness of 9 1 along the center of the apex and a Rockwell A hardness of 86 along the upper side edges. The reason for this variation in hardness is unknown but results in the apex wearing less than the sides with the result that the apex was maintained in a generally pointed condition. This is in contrast to inserts of the same shape and size, formed entirely of a WC particle base, the apices of which relatively soon wore flat, with a consequent serious reduction in the drilling speed.

The proportion of the binding agent may be varied in accordance with the desired resistance to shock and impact, and may be from to 30% of the total particles or base. In general, the higher the proportion of binding agent, the greater the resistance to shock and impact. However, the amount of the binding agent should not be increased so as to unduly decrease the hardness and consequently the wear and abrasion resistance of the product. Nevertheless, the proportion of the binder may be increased considerably over that previously used with WC inserts and still obtain as high or a higher hardness. For instance, an insert made with W C cobalt alloy (2% cobalt) particles sintered with 13% cobalt had a hardness of Rockell A 91, while an insert formed of W C cobalt alloy (2% cobalt) particles sintered with 20% cobalt had a hardness of Rockwell A 88, the latter hardness being greater than the Rockwell A 86 hardness of an insert formed of WC particles sintered with 13% cobalt. In addition, an insert formed of W C cobalt alloy (2% cobalt) particles and WC particles, in each of the proportions of 40% W 0 cobalt alloy particles and 60% WC particles and the proportions of 60% W C cobalt alloy particles and 40% WC particles, sintered with 22% cobalt had a hardness of Rockwell A 89 and 90, with some readings of Rockwell A 91. In comparison, an insert formed of WC particles sintered with 20% cobalt had a hardness of Rockwell A 82 to 84, while an attempt to form an insert of WC particles and 22% cobalt resulted in visible spots having a hardness no greater than cobalt alone. Attempts to produce a satisfactory insert from W C (without cobalt) particles and over 20% cobalt as a matrix have produced similar results, one theory to explain why 20% cobalt is the maximum for the matrix is that in excess of 20% cobalt produces a plastic flow and prevents the molded insert from retaining its shape during sintering, thus producing the visible soft spots. Apparently, by using the W C cobalt alloy, such plastic flow of the matrix cobalt is not produced and the molded insert thus retains its shape during sintering. Furthermore, inserts formed of W C particles, without alloying cobalt, sintered with 13% and 15% cobalt, respectively, and having a hardness reading of Rock-well A as high as but with some readings as low as Rockwell A 84, were found to be so brittle as to be unable to withstand successfully the shock of drilling earth formations with percussion bits.

From the foregoing, it will be evident that the novel sintered tungsten carbide products of this invention provide a longer life for cutting tools, as well as permitting the use of increased cutting speeds, the product having a much greater resistance to shock and impact than products formed entirely of WC particles having an equivalent or even a lesser hardness and also a greater hardness than WC products having the same proportion of binding agent.

Although the particles which produce the results of this invention are referred to as W C cobalt alloy particles, it Will be understood that this term encompasses an alloy of tungsten, carbon and cobalt, as described previously, since the amount of carbon, i.e., 3% to 4%, in proportion to the tungsten, corresponds to the approximate chemical formula W C. Thus, reference to a fused alloy of tungsten carbide having the approximate formula W C and cobalt in the amount of 1% to 3% also includes an alloy of tungsten, carbon and cobalt, with the carbon being from 3% to 4% and the cobalt from 1% to 3% and the remainder substantially tungsten, it being noted that impurities up to 3% may be present, particularly molybdenum.

What is claimed is:

1. A sintered tungsten carbide product for use in earth drilling tools consisting of from 30% to of crushed and ground particles of a fused alloy of tungsten carbide having the approximate formula W 0 and cobalt in the amount of 1% to 3%, and from 0% to 70% of particles of carburized tungsten having the approximate formula WC, bonded together by a lower melting point metallic material comprising from 5% to 30% of said particles and selected from the group consisting of cobalt, nickel, iron and alloys thereof.

2. A sintered tungsten carbide product, as defined in claim 1, wherein said WC particles are less than 10 microns in size and said W C cobalt alloy particles are predominantly greater than 10 microns in size.

3. A sintered tungsten carbide product, as defined in claim 2, wherein the majority of said W C cobalt alloy particles are between 30 and 40 microns in size.

4. A sintered tungsten carbide product, as defined in claim 1, wherein said W C cobalt alloy particles and said WC particles are predominantly smaller than 10 microns in size.

5. A sintered tungsten carbide product, as defined in claim 1, wherein said lower melting point metallic material comprises cobalt powder.

6. A sintered tungsten carbide product for use in earth drilling tools consisting of a mixture of from 40% to 60% of crushed and ground particles of a fused alloy of tungsten carbide having the approximate formula W C and cobalt in the amount of 1% to 3%, and from 60% to 40% of particles of carburized tungsten having the approximate formula WC; and a metallic cementing agent having a lower melting point than said particles, comprising from 5% to 30% of said particles and selected from the group consisting of cobalt, iron, nickel and alloys thereof.

7. A sintered tungsten carbide product for use in earth drilling tools, comprising a base of crushed and ground particles of a fused alloy of tungsten carbide having the approximate formula W C and cobalt in the amount of 1% to 3%, cemented together by a metallic material having a lower melting point than said particles, comprising from 5% to 30% of said particles and selected from the group consisting of cobalt, iron, nickel and alloys thereof.

8. A sintered tungsten carbide product, as defined in claim 7, wherein said metallic bonding material comprises cobalt powder.

9. A sintered tungsten carbide product, as defined in claim 8, wherein said fused alloy of tungsten carbide has the approximate formula W C and cobalt in the amount 6 of 2%, with including molybdenum in an amount not over 3%.

References Cited in the file of this patent UNITED STATES PATENTS 

1. A SINTERED TUNGSTEN CARBIDE PRODUCT FOR USE IN EARTH DRILLING TOOLS CONSISTING OF FROM 30% TO 100% OF CRUSHED AND GROUND PARTICLES OF A FUSED ALLOY OF TUNGSTEN CARBIDE HAVING THE APPROXIMATE FORMULA W2C AND COBALT IN THE AMOUNT OF 1% TO 3%, AND FROM 0% TO 70% OF PARTICLES OF CARBURIZED TUNGSTEN HAVING THE APPROXIMATE FORMULA WC, BONDED TOGETHER BY A LOWER MELTING POINT METALILIC MATERIAL COMPRISING FROM 5% TO 30% OF SAID PARTICLES AND SELECTED FROM THE GROUP CONSISTING OF COBALT, NICKEL, IRON AND ALLOYS THEREOF. 